A magnetic recording apparatus, for example a magnetic disk apparatus, includes a magnetic disk housed in a casing, a spindle motor that supports and rotates the magnetic disk, a magnetic head that writes data to and reads data from the magnetic disk, and a carriage assembly that supports the magnetic head so as to be movable relative to the magnetic disk. The magnetic head includes a slider attached to a suspension, and a head portion disposed to the slider, which has a recording head for writing and a reproducing head for reading.
Magnetic heads for perpendicular magnetic recording have been proposed to improve the recording density and the capacity, and to decrease the size of magnetic disk apparatuses. Furthermore, microwave-assisted recording heads are proposed, in which a spin torque oscillator generating high-frequency waves is disposed near a main magnetic pole to apply a high-frequency magnetic field to a recording medium.
A microwave-assisted magnetic recording apparatus needs to improve the track recording density in addition to the improvement of the recording magnetic field, and for this purpose needs a steep gradient magnetic field.
A conventional microwave-assisted magnetic heads performs recording in the following manner. The magnetic field generated by the main magnetic pole is divided into a component in the recording gap between the main magnetic pole and the trailing shield and a component on the recording medium side. If the direction of a current flowing through the recording coil is reversed, the magnetic field of the component in the recording gap is reversed in accordance with the reversal of the recording magnetic field Hr applied to the recording medium. This leads to the reversal of the magnetization of the spin injection layer in the spin torque oscillator disposed in the recording gap. As a result, the rotating direction of the high-frequency magnetic field Hac generated by the spin torque oscillator is reversed. The high-frequency magnetic field Hac rotating in a different direction in accordance with the reversal of the polarity of the recording magnetic field Hr, which is the basic principle of the assistance effect, can be obtained in this manner.
In order to achieve a steep gradient in the recording magnetic field Hr, a narrow recording gap is needed. The thickness of the spin torque oscillator disposed in the recording gap should be reduced for this purpose. However, in order to improve the intensity of the high-frequency magnetic field Hac (to improve the recording capacity), the thickness of the oscillation layer of the spin torque oscillator should be increased as much as possible. Therefore, in order to reduce the thickness of the spin torque oscillator, the thickness of the spin injection layer is preferably reduced. Spin torque oscillators in which an oscillation layer is disposed on the top of the air-bearing surface (ABS) and the spin injection layer is moved back from the ABS are proposed, as is known in the art. The area between the main magnetic pole and the trailing shield in the recording gap of the proposed spin torque oscillator is wider than that of conventional spin torque oscillators since the magnetic field in the recording gap is applied to the portion from which the spin injection layer is moved back from the ABS. This causes a problem in which the magnetic field generated by the main magnetic pole rather than the recording magnetic field Hr flows into the recording gap more easily. As a result, the recording magnetic field Hr may be reduced.